A spin-orbit torque (SOT) MRAM is a magnetic memory technology which is able to improve an operating speed to 1 ns and achieve an unlimited number of operations, and is considered as an important technology to undertake the spin torque transfer (STT) MRAM. The highest efficiency of the spin Hall effect can be achieved in a 3-nm ultra-thin heavy metal layer. Therefore, how to fabricate a 3-nm metal layer structure with high uniformity is the key to mass production.